1. The Field of the Invention
The present invention pertains to a method and apparatus for improving the economics of production from a producing well. In particular, the present invention utilizes the upstroke of a pumping system to bring to the surface the produced oil, and a portion of the produced water, and the downstroke to inject the remaining water into another, usually deeper, formation.
2. The Prior Art
There has long been, throughout the entire petroleum industry, an effort to improve the economics of production by reducing the pumping or "lifting" costs. One such attempt has been the method known as "gas lifting" in which a high pressure reservoir gas or inert gas is injected into the production tube to lower the specific gravity of the oil and thus increase the upward rate of flow. Examples of this may be found in U.S. Pat. Nos. 4,251,191 and 4,295,795. However, normally large volumes of water are produced, along with the oil, and there are associated costs in both the lifting and the subsequent handling of this produced water after it has arrived at the surface. To date the efforts to reduce the costs associated with water production have primarily been directed towards sealing off water producing layers, either with mechanical devices positioned downhole at the water producing layer or by means of chemicals or cement injected into the water producing layer.
The present invention takes a different approach which is to separate the produced oil and water downhole in an annulus formed between the casing and production tubing, lift the oil and only a portion of the water, and inject the remaining water downhole instead of trying to shut the water off. One significant benefit of the present invention is a substantial reduction in the lease costs which are directly associated with the amount of fluid lifted from a producing well. A reduction in the volume of fluid lifted for the well also results in lowering horsepower requirements, since only a fraction of the total produced fluid, namely the produced oil and only a portion of the produced water, is lifted to the surface. Also, injection power costs, water treating costs, spill containment and cleanup costs, and some maintenance costs can be expected to be significantly reduced through use of the present invention.
A somewhat similar approach to the problem of produced water is detailed in U.S. Pat. No. 5,176,216. However, this patent is addressed to a significantly different problem in that it concerns gas production. The gas, by virtue of its low specific gravity, does not require pumping to the surface for production, as is the case for the heavier petroleum products. Thus this patent is concerned with injecting produced water below a packer to keep the gas producing strata above the level of the produced water.
The subject invention also has applications with respect to waterflooding deeper zones with excess water produced from shallower zones. In typical waterflood applications, water and oil are produced by conventional methods to a battery where it is separated and temporarily stored. Then the water is pumped through a facility into an injection well. The injection wells are either strategically drilled new wells or existing wells which are converted to this purpose. In particular situations, the desired placement of injection wells is not always possible because of limiting economic factors, such as the location and number of idle wells, injection facility size, reservoir size, pipeline location, etc. The present invention may allow small scale floods or pattern reconfiguration, due to the dual utility of a single wellbore, without the attendant high costs of surface facilities.